The invention concerns a stereolithography machine of the type suitable for making three-dimensional objects by means of a plurality of superimposed layers, wherein each layer is obtained through the selective solidification of a fluid substance in the areas corresponding to the volume of the object to be produced.
A stereolithography machine of the known type comprises a container that contains a fluid substance, generally a light-sensitive resin in the liquid or paste state.
The machine comprises also a source, generally of the luminous type, which emits radiation suited to solidify the fluid substance.
An optical unit provides for conveying said radiation towards a reference surface arranged inside the container, which corresponds to the position of the layer of the object to be solidified.
The three-dimensional object being formed is supported by a modelling plate, which can be moved vertically with respect to the container, in such a way that it is possible to arrange the last solidified layer of the object in a position adjacent to said reference surface.
In this way, once each layer has been solidified, the modelling plate is moved so as to arrange again the solidified layer adjacent to the reference surface, after which the process can be repeated for the successive layer.
The stereolithography machines of the said type are divided in two main embodiments that are described, for example, in the Italian Patent application for industrial invention no. VI2010A000004, in the name of the same applicant who is filing the present invention.
According to the first one of said embodiments, the reference surface is arranged adjacent to the bottom of the container, which is transparent to radiation.
In this case, the fluid substance is irradiated from below and the three-dimensional object is formed under the modelling plate.
According to the second embodiment, the reference surface is arranged at the level of the free surface of the fluid substance.
In this second case, the fluid substance is irradiated from above and the three-dimensional object is formed over the modelling plate.
In both embodiments, the radiation can be conveyed to the different points of the reference surface using different optical units of the known type.
A first type of optical unit comprises a matrix of mirrors that can be controlled individually in such a way as to project the image of the layer of the object on the predefined surface.
In particular, each mirror can assume two different positions, an active position from which the radiation is reflected towards a corresponding point of the reference surface and a passive position from which the radiation is reflected towards a dispersion area.
Said matrices of mirrors are capable of lighting the entire reference surface at the same time, thus making it possible to obtain each layer by means of a single exposure and, consequently, in a particularly quick manner.
However, the matrices of mirrors have limited definition, with the inconvenience that objects with irregular edges are obtained.
A further drawback of the systems mentioned above lies in that the image they generate has uniform luminous intensity on its entire surface.
Therefore, this leads to the inconvenience that said systems do not allow light power to be modulated in the different areas of the reference surface.
In a second type of optical unit the radiation is conveyed to a single point of the reference surface and said point is moved in such a way as to progressively light the entire portion of the reference surface corresponding to the volume of the object.
Compared to the type of optical unit described above, this optical unit offers the advantage that it is possible to direct the light beam towards any point on the reference surface, making it cover continuous trajectories and thus obtaining objects that are free from the irregularities caused by the optical units of the type previously described.
Furthermore, this type of optical units advantageously makes it possible to modify light intensity in the different areas of the reference surface.
According to a known embodiment of the optical unit of the second type described above, a laser light source is provided that is moved on two orthogonal axes by means of a mechanical device.
This embodiment poses the drawbacks that the movements of the light beam are rather slow and that, furthermore, the mechanical device used to move the light beam runs the risk of breaking and therefore needs a certain amount of maintenance.
According to a different embodiment of the optical unit, a fixed source and one pair of galvanometric mirrors are used to direct the light beam, arranged in series one after the other.
Each mirror is motorised, in such a way as to allow it to rotate around a corresponding rotation axis that is orthogonal to the axis of the other mirror, so that the combination of their rotations makes it possible to direct the beam towards any point of the reference surface.
Compared to the known system previously described, the system just illustrated above offers the advantages that it allows the beam to be moved very quickly, which is due to the lower inertia of the galvanometric mirrors, and that it ensures more reliability, thanks to the smaller number of mechanical components used.
Notwithstanding the advantages explained above, the optical unit just described requires that the two mirrors are aligned during the construction of the machine, in such a way as to obtain the correct reflection of the light beam. In fact, in order to have the beam direction correspond to the positions of the mirrors, it is necessary that the beam be incident on both mirrors at the level of the respective rotation axes.
The above mentioned alignment operation poses the drawback that it is particularly complex and increases the cost of the stereolithography machine. Said drawback occurs also in the case where, during use, one or both mirrors break, with the consequence that it is necessary to replace them and align them correctly.
A further drawback is represented by the fact that galvanometric mirrors are relatively expensive, which considerably affects the cost of the stereolithography machine.
An optical unit based on galvanometric mirrors poses the further drawback of being relatively bulky.
The high cost and large size make the stereolithography machine unsuitable for small series applications, which might be required by small craftman's businesses.
Furthermore, galvanometric mirrors have some mechanical components that are subject to wear and therefore limit their advantages compared to the mechanical movement devices mentioned above.
Galvanometric mirrors, furthermore, are characterized by non-negligible inertia, which affects the deviation speed of the light beam and thus also the overall processing time.
The present invention intends to overcome all the above mentioned drawbacks that are typical of the known art.
In particular, it is one object of the invention to provide a stereolithography machine that offers the same advantages offered by the stereolithography machines of the known type based on the use of galvanometric mirrors and that furthermore is simpler to produce and to use compared to the latter.
In particular, it is one object of the invention to avoid the operation of alignment of the mirrors described above, both during production and during use.
The said objects are achieved by a stereolithography machine constructed in accordance with the main claim.
Further detail characteristics of the invention are illustrated in the respective dependent claims.
Advantageously, the fact that it is not necessary to provide for aligning the mirrors considerably simplifies the construction of the stereolithography machine of the invention compared to those of the known type, leading to a consequently lower cost.
It can be understood that said advantage is ensured also when it is necessary to replace the optical unit during use, leading to a reduction in machine maintenance costs.
Furthermore, to advantage, the stereolithography machine of the invention has smaller overall dimensions than the machines of the known type with equivalent potentialities.
Both the advantages illustrated above make the stereolithography machine of the invention convenient also for application in very small series, for which the stereolithography machines of the known type are not suitable.